Worry is a kind of thought and memory evolved to give life direction and protect us from danger. Without its nagging whispers, we would be prone to a reckless, Panglossian lifestyle marked by drug abuse, unemployment and bankruptcy. Why not smoke, have that last drink for the road, pollute the water supply, or evade taxes? All will be fine! In our feel-good, smiley-face era, generally free of plague, famine and war, it is easy to adopt a smug optimism and demean a behavior that has served us well throughout our evolutionary history.

In the popular media, we are constantly reminded of the presumed personal and social benefits of chirpy, unbridled optimism, and are taught to fear the corrosive effects of pessimism and worry. I speak from experience. As an expert on laughter and humor, I am frequently contacted by reporters seeking quotes for stories they have been commissioned to write about "laughing your way to health," "the power of a positive outlook," and the like. They are uninterested when I report that laughter, like speech, evolved to change the behavior of other people, not to make us healthy, and that any medicinal effects of laughter are secondary. Also unwelcome are my comments about the dark side of laughter in jeers, ridicule, and violence. In the interest of restoring balance, I accept the role of curmudgeon and defend the value of worry.

On the basis of a famous, long-running longitudinal study of 1,178 high IQ boys and girls initiated by Louis Terman in 1921, Howard Friedman and colleagues found that conscientiousness was the personality trait that best predicted longevity. Contrary to expectation, cheerfulness (optimism and sense of humor) was inversely related to longevity. In other words, conscientiousness, a correlate of worry, pays off in a long life. A modest level of worry is usually best, an instance of the U-shaped function familiar in physiological and behavioral science. Too much worry strands us in an agitated state of despair, anxiety and paranoia; too little leaves us without motivation and direction. Worry contributes life's "to do" list, but its relentless prompts are unpleasant and we work to diminish them by crossing items off the list. The list is constantly fine-tuned and updated. As life's problems are solved, topics of worry are extinguished, or if a dreaded event does not occur or becomes obsolete, we substitute new, more adaptive topics of concern. The bottom line? Stop worrying about worry. It's good for you.